linux-kernel - Re: [RFC v1 05/26] x86/traps: Add #VE support for TDX guest

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Date:   Mon, 8 Feb 2021 08:46:39 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC v1 05/26] x86/traps: Add #VE support for TDX guest

> > > So what happens if NMI happens here, and triggers a nested #VE ?
> > 
> > Yes that's a gap. We should probably bail out and reexecute the original
> > instruction. The VE handler would need to set a flag for that.
> > 
> > Or alternatively the NMI always gets the VE information and puts
> > it on some internal stack, but that would seem clunkier.
> 
> The same is possible with MCE and #DB I imagine.

I don't think there are currently any plans to inject #MC into TDX guests. It's
doubtful this could be done securely.

#DB is trickier because it will happen every time, so simply reexecuting
won't work. I guess it would need the ve info stack, or some care in kprobes/kernel
debugger that it cannot happen. I think I would prefer the later.

-Andi